This invention relates to a shuttering used for forming concrete.
Heretofore, there has been a shuttering comprising a plate and two fabrics sewed to each other and covering the surface of the plate. The two fabrics consist of an inner fabric adhered to the surface of said plate and an outer fabric which permits passage of water but prevents concrete from passing (See U.S. Pat. No. 4,730,805).
By using this shuttering, surplus water which has passed through the outer fabric contacting concrete is discharged in large quantities through the gap between the inner and the outer fabrics, so that the ratio of water to cement of the surface layer of formed concrete can be reduced and early removal of the form from concrete can be promoted. Also, the outer fabric prevents passing of part of numerous particulate substances consisting of cement particles, aggregate particles, etc. contained in said surplus water to act as a filter which leaves these between the outer fabric and the formed concrete. The residual particles later form a surface layer of high hardness.
The shuttering is cleaned to remove particulate substances adhered to both the fabrics for reuse after removing the form. The shuttering can be cleaned by jetting water toward the outer fabric, but cleaning away said particulate substances from said inner fabric was too difficult to have a sufficient cleaning effect. Thus, it was unavoidable to reuse a shuttering with said particulate substances not sufficiently removed. When the shuttering is reused, the remaining particulate substances in the inner fabric combine with particulate substances in the surplus water flowing between the inner and the outer fabrics to narrow the gap between both the fabrics, preventing the surplus water from flowing, which reduces the discharge thereof. The particulate substances remaining in the inner fabric accumulate each time the shuttering is reused, which reduces the number of reuses thereof.
Further, because the inner fabric is adhered by adhesive to said plate and the outer fabric is sewed to the inner fabric, the outer fabric hardly follows the settling of placed concrete. In view of this, during curing, there occurs a comparatively large relative displacement between the concrete surface layer adhered to the outer fabric and the deep inner portion of the concrete. This relative displacement is a primary factor to prompt separation of said surface layer from said deep inner portion when the form is removed.